Proton Effects in the Electrochemistry of the Quinone Hydroquinone System in Aprotic Solvents

Electrochemical and spectroscopic techniques have been used to study the benzo‐, duro‐, tetrachloro‐, and p‐xyloquinone‐hydroquinone couples in nonaqueous solvents. The proton transfer reactions which are coupled to the electron transfer steps are elucidated. Oxidation of the hydroquinone leads to the protonated quinone species, while reduction of the quinones in the presence of a proton source gives mixtures of the corresponding hydroquinone, its conjugate base, and the free semiquinone, depending on the amount and strength of the proton donor used. Oxidation of the hydroquinones is postulated to proceed via a dimer of the one‐electron intermediate. Preliminary results are reported on the electrochemical behavior of solutions containing the quinhydrone charge‐transfer complex.